Solvation properties of silver ions in ionic liquids using attenuated total reflectance ultraviolet spectroscopy

The solvation structures of N-butyl-N-methylpyrrolidinium dicyanamide ([BMP][DCA]) surrounding silver ions were investigated using attenuated total reflectance-ultraviolet (ATR-UV) spectroscopy. The addition of Ag+ to [BMP][DCA] red-shifted the [DCA]- absorption band. The shift direction was opposite to that caused by the addition of Li+, and these spectral shifts were qualitatively reproduced using quantum chemical calculations. Multivariate analysis (the multivariate curve resolution-alternating least squares; MCR-ALS) and molecular dynamics simulations were used to decompose the ATR-UV spectra into separate [DCA]- and Ag-solvated [DCA]- spectra. Both multivariate analysis and molecular dynamics simulation showed that the coordination number of [DCA]- around Ag+ was approximately-five. The proposed method using spectroscopic techniques, spectral decomposition, and simulations can be used for the quantitative investigation of various solvation structures, which are fundamental features in electrochemistry. (C) 2022 Elsevier B.V. All rights reserved.